This invention relates generally to laser assemblies, and more particularly to a widely tunable laser assembly with an integrated optical amplifier.
Thin fibers of optical materials transmit light across a very broad frequency bandwidth and therefore communications data from a light source may be transmitted over such fibers over broad frequency ranges. At any particular frequency, a laser source must have high output power, narrow laser linewidth and good transmission performance through great distances of optical fiber.
In higher bandwidth communications systems, where many frequencies of laser light are transmitted along a fiber, there may be one or several laser sources. While a tunable laser source would be preferred, higher data capacity systems presently use multiple laser sources operating on different frequency channels to cover the wide fiber transmission bandwidth. This is the case since appropriate laser sources are presently incapable of rapid, electronic frequency tuning without attendant deterioration of other significant figures-of-merit.
For example, at a fixed frequency, sampled grating distributed Bragg reflector (SGDBR) lasers have the high output power, narrow laser linewidth and good transmission performance necessary for an optical data network. While some SGDBR lasers can be rapidly tuned over more than 100 different transmission channels, two problems nevertheless prevent these devices from being employed in fiber optic communication systems. The most significant problem is the significant absorption of the mirror material. The resulting large cavity losses act to make the laser output power insufficient for the requirements of a present-day communications system. A second problem is that the output power and frequency tuning are dependent on each other. This coupling results in inadequate controllability for a present-day communications system.
What is needed, instead, is a device with a combination of sufficiently high output power for a high-bandwidth optical communications network and with frequency tuning controllability substantially independent of output power controllability.
Accordingly, an object of the present invention is to provide an integrated laser assembly that includes a tunable solid state laser and optical amplifier where all of the elements are fabricated in a common epitaxial layer structure.
Another object of the present invention is to provide an integrated laser assembly that includes a tunable solid state laser and optical amplifier with an output mode conditioned for transmission in an optical fiber.
Another object of the present invention is to provide an integrated laser assembly that includes a tunable laser and optical amplifier reducing optical feedback from the amplifier to the laser.
A further object of the present invention is to provide a tunable, integrated laser assembly where laser frequency control and output power control are substantially independent.
These and other objects of the present invention are achieved in a laser assembly that includes an epitaxial structure formed on a substrate. A tunable laser resonator and a separately controllable optical amplifier are formed in the common epitaxial structure. The amplifier is positioned outside of the laser resonator cavity to receive and adjust an output received from the laser, however, at least a portion of the laser and amplifier share a common waveguide.
In different embodiments of the present invention, properties of the common waveguide such as optical properties, or centerline curvature or cross-sectional are non-uniform along the waveguide centerline or non-uniform across a normal to the centerline.